NUCLEAR-MAGNETIC-RESONANCE STUDY OF SPIN RELAXATION AND MAGNETIC-FIELD GRADIENTS IN MAPLE LEAVES

H-1 Nuclear magnetic resonance techniques were used to measure the dis tributions of spin-spin relaxation times, T-2, and of magnetic field g radients in both the chloroplast and nonchloroplast water compartments of maple leaves (Acer platanoides). Results showed that encounters be tween water molecules and membranes inside chloroplasts provide an ine fficient relaxation mechanism; i.e., chloroplast membranes interact we akly with water molecules. Gradient measurements indirectly measured t he sizes of chloroplasts by showing that water in the chloroplasts is confined to small compartments a few mu m in diameter. A comparison be tween measured gradients and gradients calculated for a model leaf ind icated that chloroplasts are somewhat more likely to occupy positions along cell walls adjacent to air spaces, but also they may be found in the interiors of cells.